The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Motorized vehicles may include a powerplant that produces drive torque that is transmitted through a transmission at one or more gear ratios to a drivetrain to drive wheels of the vehicle. The powerplant may be a hybrid powerplant and may include an internal combustion engine coupled to an electric machine. During operation of the vehicle, the drive torque may be supplied by the engine, the electric machine, or a combination thereof.
Gasoline engines produce drive torque by combusting a mixture of air and gasoline. Exhaust produced by the combustion typically includes various chemical compounds, including carbon dioxide (CO2), water (H2O), nitrogen oxides (NOX), unburned hydrocarbons (HC), sulfur oxides (SOX), and other compounds. The exhaust may be treated in an exhaust system to reduce the emissions of one or more of the various chemical compounds. Vehicle exhaust systems may include a three-way catalytic converter that reduces the emission of NOX, CO, and HC in the exhaust. The catalytic converter may reduce NOX to nitrogen and oxygen, may oxidize CO to CO2, and may oxidize HC to CO2 and H2O.
Engine control and diagnostic systems may monitor the conversion capability of the catalytic converter (i.e., catalyst efficiency) to inhibit excess NOX, CO, and HC in the exhaust. The conversion capability of the catalytic converter may also be monitored to determine whether the catalytic converter is functioning properly and whether the catalytic converter should be replaced.
Oxygen storage capacity (OSC) is one measure of the conversion capability of the catalytic converter. The OSC refers to the ability of the catalytic converter to store excess oxygen under lean engine operating conditions and to release oxygen under rich engine operating conditions. The amount of oxygen storage and release decreases as the conversion capability of the catalytic converter is reduced. Therefore, the loss in OSC may be related to the loss in conversion capability. Accordingly, engine control and diagnostic systems may periodically determine the OSC of the catalytic converter.
Some methods for determining the OSC monitor pre-catalyst oxygen (O2) sensor output and post-catalyst oxygen (O2) sensor output during intrusive diagnostic tests conducted during steady-state engine operating conditions, such as during engine idle, when consistent emissions output may be achieved. The diagnostic tests include initiating an intrusive fueling event, such as a lean or rich condition, for a predetermined first period. Following the period, the diagnostic test initiates an opposite rich or lean condition for a predetermined second period. During the second period, the output of the pre-catalyst and post-catalyst O2 sensors is monitored and the OSC is computed based on a lag time between the pre-catalyst and post-catalyst O2 sensors detecting the rich or lean condition.
The output of the pre-catalyst and post-catalyst O2 sensors may also be monitored to determine whether the O2 sensors are functioning properly. A common characteristic of a malfunctioning O2 sensor is a lazy or sluggish response. Accordingly, O2 sensor responsiveness is one measure for determining whether the O2 sensors are functioning properly. Some methods of monitoring O2 sensor performance initiate intrusive diagnostic tests that initiate rich and/or lean engine operating conditions during periods of steady-state engine operation. During the periods, the output of the O2 sensor is monitored to measure the responsiveness of the O2 sensor to the changed engine operating conditions.